1. Field of the Invention
The present invention relates in general to a process for preparing a silica-based organic-inorganic hybrid resin and the hybrid resin prepared therefrom. In particular, the invention relates to a process for preparing a silica-novolac hybrid resin using sol-gel process in which phenol is used as catalyst and octamethycyclotetrasiloxane is used as modifier.
2. Description of the Related Art
Organic-inorganic hybrid resins from sol-gel process of silica-novloac have been developed recently. This kind of hybrid resins has applications in flame-retardants, thermal insulation, chromatographic packing, water filtration, ion exchange and carbon electrodes for energy storage devices. The hybrid resins are prepared by subjecting organic polymer or oligomer and alkoxides to hydrolysis-condensation reaction. The organic polymer not only can be homogeneously dispersed in the inorganic network formed but also be covalently bonded thereto. And thus the mechanical properties such as failure modulus, Yang modulus of the hybrid resins are superior due to the covalently cross-linked structure.
However, in the sol-gel process of organic carbon aerogels, acid catalysts are used. For example, U.S. Pat. No. 5,744,510 discloses a process for fabricating aerogels. The process includes reacting phenolic-novolac oligomer with furfural in the presence of toluene sulfonic acid or phosphoric acid to produce cross-linked gel. The cross-linked gel is then super-critically dried to form high surface area aerogels. Using acids as catalyst will inevitably cause ion contamination to the environment. Also, in case the amount of the formed silica clusters increases, phase separation between the organic phase and inorganic phase is easily formed. This often results in the deterioration of the physical properties, such as strength and toughness of the final product.
An object of the present invention is to provide a process for preparing inorganic-organic hybrid resin, by which process, no phase separation occurs, the gel time of the sol-gel process is reduced, and there is no need to use acids as catalysts.
Another object of the invention is to provide an inorganic-organic hybrid resin that exhibits superior physical properties.
It has been found that in the presence of phenol or phenolic resin as catalyst, the gel time of the sol-gel process of silane can be reduced and the formed silica clusters have a lower surface hardness.
Accordingly, a process of preparing a silica-based inorganic-organic hybrid resin of the invention includes hydrolyzing silane in the presence of a phenol or phenolic resin, condensing the hydrolyzed silane to obtain silica clusters, and reacting the silica clusters with thermosetting resins.
The phenol or phenolic resin has hydroxy group, and thus can facilitate the sol-gel process, which uses water as a main medium, resulting in the reduction of the gel time. Also, hydroxy groups react with the Sixe2x80x94OH and Sixe2x80x94OEt and form Sixe2x80x94Oxe2x80x94C bonds resulting in the lowering of the surface hardness of the silica clusters. Phenol or phenolic rein is actually a weak acid and thus can be used as catalyst and does not cause any ion contamination.
It has also be found that modifying the silica clusters with cyclosiloxane before they react with organic resin such as phenolic-novolac resin, can increase the toughness of the resultant inorganic-organic hybrid resin and also facilitate the sol-gel process so as to enlarge the reaction window.
Based on this finding, an improved process of the invention includes hydrolyzing silane in the presence of a phenol or phenolic resin, condensing the hydrolyzed silane to obtain silica clusters, reacting the silica cluster with cyclosiloxane, and reacting the modified silica clusters with thermosetting resins.